In many hydrocarbon wells, inflowing fluid passes through a sand screen which filters out particulates from the inflowing oil or gas. The sand screen prevents sand from entering the wellbore and reduces damage which may occur by erosion. Conventionally, sand screens are made with a metallic mesh material. Once the sand screen is placed into the wellbore, gravel packs are pumped to fill the annulus between the screen and the formation.
In other instances, some sand screens are expandable and are expanded downhole after placement in the wellbore. The result is a reduction in the annulus between the screen and the formation. The expandable screens in many instances have a limited expansion ratio and the ability of the expandable screen to conform to borehole irregularities may not be satisfactory. Further, the ability of the expandable sand screen to resist borehole collapse may be reduced. Conventional sand screens are rated to resist greater external pressure than expandable sand screens. Expandable sand screens resist less external pressure because of plastic deformation experienced by their metallic components.
Recently, self-expandable polymer screens have been developed. The sand screen comprises a cellular shape memory polymer. The cellular polymer is compressed and stored in a collapsed foam form. It is then placed into a wellbore and expanded by raising a temperature or pumping a triggering fluid. The foam material once in the borehole softens and tries to return to its original expanded shape. The expansion outer diameter was designed to be higher than the borehole internal diameter, resulting in the foam conforming to the borehole. The polymer matrix composing the foam is a thermoset that goes through glass transition and becomes rubbery, releasing internal stresses and therefore expanding the cells. The compliant foam has a large expansion ratio, which depends on the porosity, and as a result can conform to the borehole.
The main advantage of these sand screen systems is compliance and their ability to expand and contact the borehole along the entire length of the borehole even in situations where the borehole is irregularly shaped e.g., uncased borehole, avoiding the need to pump gravel slurries. One of the disadvantages of the foam material used in these sand screens is the weak mechanical properties of these foams. The collapse pressure for a tube made of this foam is lowered when the material is more compliant and the foam is less dense. Screen collapse under wellbore pressure may lead to a loss of permeability and a stuck completion string in the wellbore which may be hard to repair or change.